How to Insulate and Air Seal an Attic Hatch
Use multiple layers of rigid foam insulation, high quality weatherstripping, and several secure latches
There’s a subset of issues in the realm of home efficiency that falls into the category “out of sight/out of mind.” The boiler in the basement, how much insulation is in the attic … as long as these issues stay out of your view, no problem. So what’s up with attic hatches, then?
Even though attic hatches can be huge air leaks and sources of radiant heat loss, they are rarely fixed. An attic hatch is usually located in a hallway or closet where the homeowners see it daily. Yet...
I mean, once the homeowners fire up a blower door and whip out their infrared camera, the problems with attic hatches are pretty obvious. Wait — what … ?
That is the stealth problem with attic hatches; they appear fine but are actually a huge heat loss. An attic hatch can have finished trim and paint, look perfect, and still be a giant heat sinkWhere heat is dumped by an air conditioner or by a heat pump used in cooling mode; usually the outdoor air or ground. See air-source heat pump and ground-source heat pump.. In the summers, it will radiate heat down into the house and in the winter, heat and warm air will escape. So what to do?
The goal is two-fold: air sealing to prevent air-transported heat loss and beefing up the insulation. No puny single fiberglass batts for us. For the purpose of this, we’re assuming an uninsulated 2′ x 2′ plywood hatch with finish molding over the rough-cut hole.
BLOGS BY ERIC NORTH
How to insulate and air seal an attic access hatch
Air seal the trim – The first step is air sealing the finish trim and enclosure around the attic hatch. Carefully pull down the finish trim. (Pray that the installer used finish nails and not, say, ring-shank nails.) Set aside the trim and, using caulk for smaller gaps (less than 1/4″) or foam sealant for larger ones, seal the gap between the attic hatch framing and the rough cut drywall. (I have to be just a shade vague there, as the drywall can either butt up against the hatch frame or lap over it).
Apply a bead of caulk on the inside and outside edges of the trim, and then reattach it.
Air seal the hatch perimeter – The plywood hatch rests on a small wood strip lip. The standard air sealing recommendation is to install a compression bulb weatherstrip. This can also be beefed up to a sealing gasket like the one on your refrigerator door. Gaskets are generally more durable and produce a tighter seal.
Insulate the hatch – Cut foam board to 1/2″ less than the size of the hatch on each side. Foil-faced polyisoPolyisocyanurate foam is usually sold with aluminum foil facings. With an R-value of 6 to 6.5 per inch, it is the best insulator and most expensive of the three types of rigid foam. Foil-faced polyisocyanurate is almost impermeable to water vapor; a 1-in.-thick foil-faced board has a permeance of 0.05 perm. While polyisocyanurate was formerly manufactured using HCFCs as blowing agents, U.S. manufacturers have now switched to pentane. Pentane does not damage the earth’s ozone layer, although it may contribute to smog. is the greenest and best-performing of the rigid foam options. Apply a bead of foam-compatible glue to it and attach it to the plywood hatch. Wash, rinse and repeat until you have added at least 4 inches of foam (but preferably 8 inches + of foam).
Fasteners – Add a handle and several hook-and-eye fasteners situated so that when the hatch is forcefully pulled down, it tightly compresses the gasket.
Attic hatches are the “Purloined Letter” of house efficiency problems. They’re in plain sight but rarely addressed adequately. Insulate and air seal your attic hatch to save money and improve your house’s comfort.
- Fine Homebuilding
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